Regarding the flippers, make sure they are aligned with the lane guides. A lot of games, mine included, had misadjusted flippers that pointed down too much. This will make the gap wider and make it harder to trap the ball.
Are you placing the level on the playfield when leveling the game? If not, you may not have the game level.
Are you setting the slope using the bubble level by the shooter lane, or using a level to make sure it is the proper slope?
All the above things can drastically affect how the game plays if they aren't done right.